The present invention relates to TDM (time division multiplexing), and more particularly to a TDM scheme for use with a digital video signal.
In digital video systems, a video signal is digitized (sampled and then quantized) before further processing. In order to achieve adequate horizontal and vertical resolution at a reasonable sampling rate at the possible expense of diagonal resolution, the sampling signal can have a 180 degree phase shift between adjacent television scanning lines. Such a sampling scheme is used in sub-Nyquist encoding such as disclosed in "Sub-Nyquist Encoded PCM NTSC Color Television" by John P. Rossi in the book "Digital Video," a review of SMPTE papers, and in a system known as "2+2" disclosed in U.S. patent application Ser. No. 168,077 filed July 14, 1980 in the names of R. A. Dischert and G. A. Reitmeier entitled "Data Rate Reduction for Digital Video Signals by Subsampling and Adaptive Reconstruction," and assigned to the assignee of the present application. In the "2+2" system every other sample is discarded and steering bits are transmitted that indicate which combination of surrounding samples is the closest match to a discarded sample. Because of said phase shift, the position of the sampling instants on a display screen form a "checkerboard" pattern as shown in FIG. 2 of said application.
The above-described sampling operation can be applied either to the composite television signal or to component television signals, such as Y, I, and Q or Y, R-Y, and B-Y. Because of the greater bandwidth of the luminance (Y) signal as compared to the chroma signals (I, Q, R-Y, and B-Y) it is typical to sample the Y signal at a rate twice that of chroma signals. For further processing it is necessary to transmit the component signals within a television studio and possibly between studios. Further it may be necessary to transmit steering bits. If so, it is desirable to transmit a single set of steering bits for all three component signals such as disclosed in U.S. patent application Ser. No. 171,379, filed July 23, 1980 in the names of R. A. Dischert and G. A. Reitmeier and assigned to the assignee of the present application. However even if only a single set of steering bits, or even no such bits are transmitted, parallel transmission of all three or four signals is wasteful of interconnecting channels or cables. Further in the above-mentioned systems, the samples may not occur at regular intervals either within or between lines, thus making decoding difficult.
It is therefore an object of the present invention to provide a TDM system, particularly one useful with a digitized television signal.
It is another object to provide a TDM system that is easy to decode.